1. Field of the Invention
The present invention relates to a method and to an arrangement for monitoring a regenerator for pseudo-ternary digital signals which contains a code rule violation checking device with a fault counter and which, at at least two inner terminals, produces two amplitude regenerated unipolar pulse trains and time regenerated universal pulse trains, one of which represents the positive input pulses and one of which represents the negative input pulses.
2. Description of the Prior Art
By combining a plurality of digitized speech signals or data signals to form a time division multiplex (TDM) signal and by combining a plurality of TDM signals, one finally obtains digital TDM signals having bit rates which can amount to a few hundred Mbit/s. TDM signals of this type are frequently transmitted as pseudo-ternary digital signals via copper cables because of the freedom of the transmission signal from direct current, in which case the transmission signal is frequently converted by means of an AMI code. Within the transmission link, pulse regenerators which undertake the amplitude-wise regeneration and time-wise regeneration of the transmission signal are interposed into the cable at specific intervals. The AMI code is characterized in that it consists of a pseudo-ternary code in which binary zeros are transmitted as zero elements and binary ones are transmitted alternately as plus and minus signals with a logic one level, and the polarity of the consecutive one pulses in each case changes. In the regeneration, a first unipolar pulse train is regenerated from the positive one-signals, and a second unipolar pulse train is regenerated from the negative one-signals, and the two pulse trains are regenerated amplitude-wise and time-wise separately. The regeneration is frequently effected using clocked D flip-flops and in the event of specific requirements on the amplitude regeneration, the D flip-flops are preceded by amplitude filters. Then, a code conversion is carried out for the regenerated unipolar pulse trains to form a new transmission signal represented in the AMI code. With respect to simple generation of such a signal by means of a quarter-wave stub line short-circuited at the end, in the regenerator it is desirable to convert the unipolar pulse trains into a signal represented in the binary difference code. The code rule for this code consists in that a logic one in the binary output signal is marked as a change in the logic level from zero to one or from one to zero in the binary difference code, whereas the logic zero in the binary output signal is marked as a retention of the logic level one or zero from the previous bit in the binary difference code. The operation of such a digital transmission system employing a transmission signal represented in the AMI code is monitored by using the redundancy of this code which, in fact, has at its disposal, three digital values of which, however, for the information transmission, two are used for the same state of the original signal. Employing the special property of the AMI code that the consecutive one-pulses must always occur with different polarity, by means of a code rule violation checking device it is possible to monitor the transmission signal, even when the same is scrambled by a pseudo-random sequence. An example of such a code rule violation checking device contained in a PCM regenerator is described in more detail in a parallel application, Ser. No. 284,987, filed July 20, 1981. In the event that this code rule violation checking device does not emit an error indication via a following telemetry device to an analyzing central control unit, in addition to the possibility of absolutely fault-free transmission of the digital signal, there is also the possibility of a breakdown in the code rule violation checking device. The check is further impeded by the following fact: in order not to disturb the operation, only those faults which do not change the communication to be transmitted can be deliberately inserted for test purposes in the transmitting station. However, such faults could merely be code rule violations. In systems of the kind described, however, all the code rule violations are completely removed from each intermediate regenerator. It is therefore impossible to check system of this type by means of special fault signals transmitted from the end station.